1. Field of the Invention
The present invention relates to a method of growing a nitride single crystal, and a method of manufacturing a nitride semiconductor light emitting device.
2. Description of the Related Art
In general, group III nitride semiconductors have received attention as materials used to manufacture visible light and ultraviolet ray LEDs configured as a light emitting diode (LED) or a laser diode (LD), and a blue-green optical device. In order to manufacture optical devices including these nitride semiconductors, a technique that grows high-quality single crystal thin films from group III nitride semiconductors is necessarily required. However, since substrates that match with lattice constants and thermal expansion coefficients of the group III nitride semiconductors are not commercially available, a method of growing a single crystal thin film is very limited.
According to the related art, examples of a method of growing a group III nitride semiconductor may include a method of growing a nitride semiconductor on a sapphire substrate (Al2O3) of a heterogeneous material by heteroepitaxy using Metal Organic Chemical Vapor Deposition (MOCVD) and Molecular Beam Epitaxy (MBE). However, a nitride single crystal is known to have a crystal defect of approximately 109 to 1010 cm−2 due to a difference in lattice constant and thermal expansion coefficient between the sapphire substrate and the nitride layer even when a low-temperature nucleation layer is used.
In order to lower crystal defects of the group III nitride semiconductors, lateral epitaxial overgrowth (LEO) is used. FIGS. 1A through 1D illustrate a method of growing a nitride semiconductor using LEO.
First, as shown in FIG. 1A, a low-temperature grown GaN buffer layer 13 is grown on a sapphire substrate 11, and then a dielectric mask 15 having a stripe pattern is formed thereon. The dielectric mask 15 is formed by depositing a dielectric material, such as SiO2 or SiNx, and patterning the deposited dielectric material to form stripe patterns at regular intervals by using a photolithography process.
A nitride single crystal growth process is performed on the GaN buffer layer 13 having the dielectric mask 15 formed thereon by using the LEO. A nitride single crystal 17′ is only grown in a window region a between the dielectric mask. If a height of the nitride single crystal 17′ exceeds a height of the dielectric mask 15, the nitride single crystal grows laterally on the dielectric mask 15 as shown in FIG. 1C. As shown in FIG. 1D, the lateral growth leads to a growth of the nitride single crystal 17 over the dielectric mask 15.
Most of the dislocations in the buffer layer 13 are blocked by using a single crystal 17b that is grown along a horizontal direction, which is different from an initial direction in which dislocations propagate. Therefore, a nitride semiconductor layer having excellent crystallinity can be formed by using the LEO. For example, the potential density of the single crystal 17b on the dielectric mask 15 may be reduced to 106 cm−2. However, this region with a low dislocation density is limited to the upper region 17b of the dielectric mask 15. A region where the dielectric mask 15 is not formed has a relatively high dislocation density. When the LEO according to the related art is used, the dislocation density is not uniform despite the region with the low dislocation density. Therefore, there has been a need for the development of a method of growing a nitride single crystal having a uniform and large area with a low dislocation density.